Spatio-temporal study of the deviations from thermal equilibrium in a high-pressure mercury plasma working under an ac power supply

This work deals with the study of deviations from thermal equilibrium in high-pressure mercury discharges operating in ac mode. A one-dimensional time-dependent fluid model assuming a non-equilibrium plasma (two-temperature code) has been developed. This code solves, self-consistently, the set of hydrodynamic equations describing the discharge plasma, coupled with an equation describing the power supply circuit. This code is based on a finite-element method and it has been optimized in order to keep CPU times realistic. Our calculations at an industrial 50 Hz frequency, validated by using experimental data from the literature, allow us the possibility to better understand the mechanisms that are responsible for deviations from thermal equilibrium within an ac cycle. Furthermore, a parametric study allows us to study in detail the influence of some key parameters, such as frequency and mercury load on those deviations.